From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-17.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id EAC46C07E95 for ; Tue, 20 Jul 2021 02:34:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D111861166 for ; Tue, 20 Jul 2021 02:34:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231126AbhGTBxT (ORCPT ); Mon, 19 Jul 2021 21:53:19 -0400 Received: from mail.kernel.org ([198.145.29.99]:33036 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1344437AbhGTBju (ORCPT ); Mon, 19 Jul 2021 21:39:50 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 5A48260C40; Tue, 20 Jul 2021 02:20:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1626747625; bh=wJQJYy19JoNbPgnn5nAMu95up14zFfvr3My3xlcpouQ=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=g27orC+9SZy5A5AyJwWySl1PbZkF4xBfGEyBSTEUOeFGKG8DWNejQVDq4Um65wCWy q1XwZU5b7s3gk4fAXP2A7OFkWPq12rhBAZp+QAkiUd2QuEx08deGizr21VTaWmDAso 5FctEeNmHPZxozCzy7MWEZNfmK4nzesvRzKXU4rsq8knw7iXI1JVuo71GyFHYEsBJI ysi2w0+hRSbDWuiWYmZfR5ZvPGhTRsxZREGO5Y2OTNJXlE7eolLT0G+2KZ56rK1Gvh VNa2BHtw0o/c2Pwi5VC+M93L9rGi3MyvNjvV/oLhXDTrte1NPzkbMVIJw6ioV72t84 I++4eraSFOaKw== Date: Mon, 19 Jul 2021 19:20:24 -0700 From: "Darrick J. Wong" To: Xiyu Yang Cc: linux-xfs@vger.kernel.org, linux-kernel@vger.kernel.org, yuanxzhang@fudan.edu.cn, Xin Tan Subject: Re: [PATCH] xfs: Convert from atomic_t to refcount_t on xlog_ticket->t_ref Message-ID: <20210720022024.GI23236@magnolia> References: <1626517262-42986-1-git-send-email-xiyuyang19@fudan.edu.cn> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1626517262-42986-1-git-send-email-xiyuyang19@fudan.edu.cn> Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org On Sat, Jul 17, 2021 at 06:21:02PM +0800, Xiyu Yang wrote: > refcount_t type and corresponding API can protect refcounters from > accidental underflow and overflow and further use-after-free situations. > > Signed-off-by: Xiyu Yang > Signed-off-by: Xin Tan > --- > fs/xfs/xfs_log.c | 10 +++++----- > fs/xfs/xfs_log_priv.h | 4 +++- > 2 files changed, 8 insertions(+), 6 deletions(-) > > diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c > index 36fa2650b081..1da711f1a229 100644 > --- a/fs/xfs/xfs_log.c > +++ b/fs/xfs/xfs_log.c > @@ -3347,8 +3347,8 @@ void > xfs_log_ticket_put( > xlog_ticket_t *ticket) > { > - ASSERT(atomic_read(&ticket->t_ref) > 0); > - if (atomic_dec_and_test(&ticket->t_ref)) > + ASSERT(refcount_read(&ticket->t_ref) > 0); > + if (refcount_dec_and_test(&ticket->t_ref)) I thought the refcount functions already had code to warn about refcounts that get decremented below zero... > kmem_cache_free(xfs_log_ticket_zone, ticket); > } > > @@ -3356,8 +3356,8 @@ xlog_ticket_t * > xfs_log_ticket_get( > xlog_ticket_t *ticket) > { > - ASSERT(atomic_read(&ticket->t_ref) > 0); > - atomic_inc(&ticket->t_ref); > + ASSERT(refcount_read(&ticket->t_ref) > 0); ...and can't come back from the dead? Also, how much of a performance impact does this have over the atomic_t functions? The last time anyone proposed conversions similar to this, there were concerns about that. --D > + refcount_inc(&ticket->t_ref); > return ticket; > } > > @@ -3477,7 +3477,7 @@ xlog_ticket_alloc( > > unit_res = xlog_calc_unit_res(log, unit_bytes); > > - atomic_set(&tic->t_ref, 1); > + refcount_set(&tic->t_ref, 1); > tic->t_task = current; > INIT_LIST_HEAD(&tic->t_queue); > tic->t_unit_res = unit_res; > diff --git a/fs/xfs/xfs_log_priv.h b/fs/xfs/xfs_log_priv.h > index 4c41bbfa33b0..c4157d87cea4 100644 > --- a/fs/xfs/xfs_log_priv.h > +++ b/fs/xfs/xfs_log_priv.h > @@ -6,6 +6,8 @@ > #ifndef __XFS_LOG_PRIV_H__ > #define __XFS_LOG_PRIV_H__ > > +#include > + > struct xfs_buf; > struct xlog; > struct xlog_ticket; > @@ -163,7 +165,7 @@ typedef struct xlog_ticket { > struct list_head t_queue; /* reserve/write queue */ > struct task_struct *t_task; /* task that owns this ticket */ > xlog_tid_t t_tid; /* transaction identifier : 4 */ > - atomic_t t_ref; /* ticket reference count : 4 */ > + refcount_t t_ref; /* ticket reference count : 4 */ > int t_curr_res; /* current reservation in bytes : 4 */ > int t_unit_res; /* unit reservation in bytes : 4 */ > char t_ocnt; /* original count : 1 */ > -- > 2.7.4 >